1. Field of the Invention
This invention relates to a camera having automatic exposure control functions with automatic focusing functions in optimum relationships.
2. Description of the Prior Art
There have been many previous proposals for different versatile automatic exposure modes (hereinafter referred to as "AE" modes) in a single camera, and a wide variety of cameras having such multi-mode versatility are now available. The AE modes heretofore used in the art may be broadly divided into three categories called a shutter speed priority automatic exposure mode (hereinafter referred to as ("Tv-AE"), an aperture priority automatic exposure mode ("Av-AE") and a programmed automatic exposure mode ("P-AE"). Of these three typical modes, the selection of Tv-AE allows the photographer to preset a desired shutter speed in accordance with which an aperture value is automatically determined. Therefore, it is suited for shooting a fast-moving object, for example, in sport photography. Alternatively, when in Av-AE, for any aperture value the photographer presets, the camera sets a corresponding shutter speed, as it is often used in portraits or other still-life photography. The P-AE, on the other hand, automatically sets both shutter speeds and apertures. Strictly speaking, however, there are roughly two ways in which the combinations of shutter speeds and apertures are programmed. One method is that as the object brightness changes, the shutter speed changes at a smaller rate than that at which the aperture changes. This may be called a shutter speed leading programmed automatic exposure mode (hereinafter referred to as "Tv-P-AE"). With the other method, the aperture changes at a smaller rate than that at which the shutter speed changes. This may be called an aperture leading programmed automatic exposure mode ("Av-P-AE"). Similar to the above-described Tv-AE and Av-AE, the Tv-leading and Av-leading aspects of the P-AE are respectively suited for in-action and at-rest photography.
Since automatic focusing control capability has recently been developed and auto-focus cameras have appeared on the market, an increasing number of automatic focusing control systems (hereinafter referred to as "AF" systems) are proposed. These AF systems operate, broadly speaking, in a servo mode, or in a one-shot mode. The servo mode is when the AF system is always in operation focusing the camera sharply on an object in spite of the moving object. In other words, after the in-focus condition has once been established when the object changes its position, the AF system moves the photographic objective again until the image of the object in the new position is sharply focused. As long as the object lies in the target area for the camera range finder, the in-focus condition is always retained. Accordingly, the servo mode is suited for use in shooting a moving object. Another or one-shot mode is such that as the photographic objective moves effecting focusing on shorter object distances, when an in-focus condition is detected, the AF system arrests the objective and despite the object distance is later changed denying readjustment of the object position. The user of this mode allows the photographer to make compositions with the subject of principal interest taking its place outside the range finding spot, which is generally positioned at the center of the entire picture frame. Therefore, the one-shot mode is suited for portraits, landscapes, or other still-life photographs.
Although two automatic focusing modes are known as described above, all the commercially available auto-focus cameras have only one mode. A camera operating with the selection of two modes, namely, a servo mode and a one-shot mode, may be considered. Since, in this situation, however, a mode selector is necessary, such an AF system is installed in a camera of multi-exposure mode versatility. Some means must be provided for automatically selecting either the servo or the one-shot mode depending on the preselected automatic exposure mode or Tv-AE, Av-AE, Tv-P-AE and Av-P-AE. Otherwise, camera management becomes very troublesome.
An object of the present invention is to provide a camera having a multi-exposure mode and a multi-focusing mode and a multi-focusing mode versatility with automatic means making it possible, upon preselection of one of the exposure modes which is suited to shoot a moving object to set the AF system in the corresponding focusing mode. Upon preselection of one of the automatic exposure modes, which is suited to shoot an object at a standstill, the AF system is also set in the other mode. Thereby, the manageability of the camera is greatly improved.